Press conference at the Royal Automobile Club, central London. Barry Hearn, new chair of the World World Professional Billiards and Snooker Association, is giving it large, talking about how he's going to reinvent the game – more fun, more fast formats, more money. "No characters in this game? Look at Ronnie, I've loved him since he was 12. Total nutcase, but what a character." Ronnie O'Sullivan smiles.

O'Sullivan, widely regarded as the most gifted player the game has known, is sitting to Hearn's left. John Higgins, the world champion, is to his right. "These boys are the luckiest in the world, so what you've got to do is love every second and thank God you've got the ability to take part in such a prestigious tournament," Hearn says. He means the World Championship, which starts at the Crucible Theatre in Sheffield this morning.

Press conference over, O'Sullivan runs out of the venue. "I really don't feel like playing in the Worlds. Couldn't wait to get out of there." Classic Ronnie. He's never been your bottle-half-full type.

It's his afternoon with his two young kids, Lily and Ronnie Jr, and he doesn't want to be late. O'Sullivan recently split up from their mother. "When you've got kids it's not ideal, but I'd rather be single than living with someone that you're just not getting on with." He is living by himself and has bought a house 19 doors away from his mother, Maria, in Chigwell. The two have always been inseparable.

The chauffeured car is stuck in traffic, so we jump out at Holborn and catch the tube. It's packed, but this doesn't stop people spotting O'Sullivan. "Excuse me, I know this is a strange question, but are you Ronnie O'Sullivan?" says one fellow traveller. Ronnie grins and fesses up. Another man stops as he's getting off, and sticks out a paw. "Nice to have met you Ronnie," he says.

At home, he says he's been a sucker yet again. One of his former managers told him he needed a big kitchen and so he went out and got himself something he doesn't want. "He goes: 'Get a new cooker, get that' and I'm thinking he must be right cos he's right on everything, but he ain't." People fall in and out of favour in O'Sullivan's world. Managers, coaches, friends come and go. I've known him nearly 10 years, and ghost-wrote his autobiography. We've always got on well, but for months he'll not get in touch then he'll call in the middle of the night. The upside is that he's warm and generous; if I was in trouble, he'd be a good person to call – so long as he answers in the first place.

He changes out of his suit into jeans and T-shirt. O'Sullivan is ridiculously fit these days. There was a time when he had any number of chins and spent every night competing with himself over how much Chinese food he could eat. Now he's a running obsessive. He runs six miles a day – at around six minutes a mile. He started running because it was something to do, and then found it helped his depression and he came off the Prozac.

We're in his Mercedes, headed for his former partner's house to collect the kids. Lily decides she'd rather stay with mum. Ronnie Jr happily gets in the car. He's handsome and funny with great round eyes, just like O'Sullivan at that age. "I'm not a snooker player, I'm big Ronnie," is the first thing he says to me.

O'Sullivan's private life is turbulent. It has been ever since his father was convicted of murder and given a life sentence when he was 15. A year later, Maria was sent down for tax evasion and Ronnie was left to look after his little sister, Danielle. For nine years he was with Jo, but now that's over and he's not pleased that he gets to see his children only for a few hours on Wednesdays and Saturdays. On the positive side, after 18 years in jail, his father, who has been on weekend release for some time, is due out any month.

In the car O'Sullivan is talking about his school days. I'd always assumed he hadn't cared about academic work (he left without qualifications) but he says that's not true. "You know what, I loved history. And as soon as they told me you're not in the top class, that was it, my days were over at school. I put my heart and soul into that. When I got 44% for my exam it killed me. I was 13." If he were to go back to school now, he says, he'd study cooking.

We meet Maria at the deli. O'Sullivan is licking smoked salmon and cream cheese off Ronnie Jr's face. It's a disgusting sight, but the two Ronnies are in raptures. "Is that 'orrible? Has Daddy got bad breath?"

For a while, O'Sullivan has said that his form is not what it was. He says his alignment is wrong, he doesn't release the ball properly with his right hand (that's why he plays left-handed, so often), he makes too many mistakes. A decade ago he was saying much the same thing and threatening to retire. But his attitude has changed.

"It's a job, innit. This year I took the attitude that I don't expect anything, just go and play, and if you win great, if you lose so what, go home, enjoy your little life away from the table. It gives me choices, it enables me to travel. See, if I can keep on playing for the next five-six years, it's irrelevant whether I win tournaments or not, that's going to be a result for me. If I stop playing, what am I going to do with my time? Even if I'm not enjoying the snooker, it still fills that time up. When I get up in the morning, I'll get down the snooker club 10.30am, play till 1.30-2, go down the gym and have a run, and 4.30 done. Do a bit of cooking. I've filled me day up. It's all about filling your day up."

Does the thought of not playing frighten him? "Yes. Absolutely. Frightens the life out of me, cos that's my trade."

Does Maria think he'll keep playing? "I think he'll give it another few years," she says. "Maybe 39-40. I'd like him to retire gracefully. I think John Parrott is making a bit of a twit of himself."

What if he was, say, 67 in the world? "He'd go before that, wouldn't you Ron?"

"Yeah," says O'Sullivan. "If I drop outside the top 16 I'm gone."

Does Maria think the game makes him happy or miserable? "Both. It's a love-hate relationship because he's such a perfectionist. He could win the World and if he's not happy with his game that's it. He's like my dad, he was a perfectionist too."

Are there new players who excite him? He shakes his head. "No. There ain't no one. No one's coming through who you watch and get a buzz off. They don't excite you like Alex Higgins – you watched him and it was like watching a thriller. But you watch Steve Davis or Stephen Hendry, John Higgins, amazing players, the greatest players ever to have picked a cue up, and you feel like you're watching Countdown. I like Countdown, but I'm not on the edge of my seat. When you watched Higgins, anything could happen and snooker needs that. It's like Usain Bolt, anything can happen, Tiger Woods, Messi exactly the same. They've got that something about them." He could add himself to the list.

What will he do when he does retire? He talks about business and the properties he owns with his mother (she has sold the family sex shops, but still owns the properties), and the possibility of doing some broadcasting work, but ultimately the children are his priority.

"The more time I can get to spend with him and little Lily … I wanna get him on the golf course, I wanna get him hitting the ball 380 yards and I'm telling you what, he could be the best golfer in the world. Look at the shoulders on him. He's got a proper little physique and what with my background in sport and my dad's motivation he's got the best start in the world."

No pressure then? He grins. "You know like they train these SAS to cope with all situations and conditions, that's what he's going to be like. He'll get on that golf course and intimidate them from the off. Like Tiger."

While Ronnie Jr is trying to electrocute himself with the TV wires, Ronnie Sr calls from prison. Maria's got three distinct tones for her Ronnies – tender for little Ron, gently questioning for Ronnie and gruff for Ronnie Sr. "Simon's here, you wanna speak to him," she says down the phone. She passes it over. Ronnie Sr tells me he's doing well and asks what I think of Ronnie Jr. "He's No1 he is," he says.

There was a time when O'Sullivan hated playing in front of his father. "He used to ruin me. Drive me mad. It killed me. He wouldn't do that now." He humiliated him when he played bad shots? "He did when I started out. It stopped when I was 12. When he stopped coming to see me I started winning. He can't help it, he's a very pushy man. Not in a horrible way."

It's early evening, and we're off to Southend to see a foot specialist – O'Sullivan's foot has been playing up for a few weeks, possibly a result of all the running. His Merc is scarily powerful – 6.5 litres. What happened to the Bentley he recently bought? "I sold it. It wasn't me."

He's on the hands-free to his father's lawyer who tells him that Ronnie Sr could be out by May or June. "I can't wait. I'll have someone to bounce off. I'll be able to tell him my innermost secrets. Maybe that's what I need, someone who'll motivate me."

O'Sullivan says he still has concerns about when he comes out. "There are times when I think: 'Cor he's a strong character', and he's still telling me what to do. I said to him: 'Dad, you can't tell me what to do. I'm 34 now, I've got my own way of doing things.'" How did he take it? "Well. I'm always going to be his son and dads are always going to be telling their boys, but I don't need someone to keep telling me what I already know. I don't want to be mothered or fathered at 34."

What type of things does his dad tell him? "Just little things. Like relationships. Do this, do that, and I just want to have a laugh with him because he's funny and I enjoy being around him. I don't want to get too wrapped up in the heavy stuff. My Dad's very 'it's all about the winning' and I'm not in that frame of mind at the moment. I said: 'Dad, whatever decisions I make, whether I play snooker, don't play snooker, do this, do that, all I want is you to be there as my Dad, as a support. That's all I want – your backing.' And he went 'You've got it.'"

Does he still worry that when his father starts watching him play again it will inhibit him? He grins. "No, he watched me in Wales."

How come the cameras didn't spot him? "No one knew he was there. He was right at the back. I was playing John Higgins, it was quite a big game and I thought it's been a long time to wait for that moment but, you know what, it's all been worthwhile. It felt great having him there. When I was a kid I still had it all to prove. There was pressure on me to impress him, to make him proud of me, whereas now I know he's proud of me."

What's moving about the way O'Sullivan talks about his father is that despite the 18 years away he still regards them as a team. "If I never potted another ball I think he'd be really happy with what we've achieved together."